Process for making manganous carbonate



United States Patent 3,262,752 PROCESS FOR MAKING MAN GANOUS CARBONATE William G. Moore, Midland, Mich., and William E. Domniug, Arvado, Colo., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed June 12, 1963, Ser. No. 287,192

6 Claims. (Cl. 23-61) The invention relates to an improved method of making manganous carbonate of improved physical properties and of high purity.

Manganous carbonate having the chemical formula, MnCO is an important industrial chemical. Among its uses is that of making Mn0 which may be accomplished by merely heating the MnCO in the presence of excess oxygen gas, e.g., air.

One of the principal uses of MnO is in the manufacture of the type of galvanic cells known generally as dry cells wherein the electrolyte consists of an aqueous paste of an electrolytic salt, e.g., NH4C1, and a depolarizer intermixed therewith, the preferred material therefor being MHO2.

Presently known methods of making lVIuCO have produced a material having a bulk density which is not satisfactory for a large number of uses among which is that of making MnO MnCO made according to a known method, e.g., by merely admixing aqueous solutions of Na CO with a manganous salt, e.g., MnCl to produce MnCO as a precipitate, and separating the precipitate,

has a bulk density usually not greater than about 10 grams (and frequently lower) per cubic inch. It is desirable that MnCO have a bulk density of .at least about 15 grams and preferably atleast about 20 grams per cubic inch. (It is customary in the trade to state the density of this type of product in grams per cubic inch, i.e., metric weight units per English volume unit.)

The principal object of the invention is to provide a method of making MnCO having the above designated desired density. The manner of carrying out the invention to attain this and related objects is made clear in the ensuing description and is succinctly defined in the appended claims.

The invention, accordingly, in a broad sense, is the method of preparing high density MnCO by an improved and heretofore unknown process which comprises admixing aqueous solutions of a water-soluble manganous salt with a water-soluble carbonate in relative proportions of each to provide and maintain a molar excess of the Mn fraction of the manganous salt over the CO fraction of the soluble carbonate therein, at a pH value of between about 5.7 and about 7.2, under stirred conditions, at a temperature of between about 55 C. and the boiling temperature of the admixture, to produce MnCO in suspension to make a slurry; maintaining the MnCO in suspension until the particle size and the concentration of the suspended MnCO in the slurry are such as to insure a bulk density of the MnCO of at least 15 grams per cubic inch, and preferably at least about 20 grams per cubic inch; and separating the MnCO so produced.

The bulk density of the MnCO product may be determined by one of several procedures, two of which are set out in detail hereinafter.

The conditions requiring a molar excess of Mn over CO i.e., a molar ratio of Mn to CO of more than 1, and the specified temperature requiring a temperature not lower than about 55 C. are critical. When these conditions are not observed, there is an objectionable amount of Na CO and/0r NaHCO occluded in the MnCO product. The pH limits must also be observed. Since Na CO raises the pH and MnCl lowers it, the pH is easily adjusted by regulating the flow of feed within the "Ice required molar ratio. The period required for obtaining proper density MnCO is at least about 1.5 hours; usually 3 to 5 hours are employed. Thev concentration of the aqueous feed solutions are not critical. However, it is recommended that the concentration be at least about 5% by weight and preferably that it approach the saturation point of the solutions at the temperature employed.

A preferred mode of practicing the invention is to admit metered flows of aqueous solutions of Na CO and MnCl of a concentration of say at least about 10% by weight, into a stirred reactor, at a rate to provide more than 1 but not appreciably over about 1.05 moles of Mn per mole of CO groups, at .a reactor temperature of between about C. and about C. and a pH value of be tween 6.0 and 6.9, to produce a MnCO slurry; periodically obtaining the bulk density of the manganous carbonate being produced in suspension; and when a bulk density of at least about 20 grams per cubic inch has been obtained, providing an overflow of slurry from the reactor and continuing to maintainthe feed, temperature, pH value, and overflow to provide an inventory time in the reactor which will continue to produce manganous carbonate of a density of at least about 20 grams per cubic inch.

One satisfactory procedure for ascertaining the bulk density of the MnCO being produced is as follows: 1000 milliliters of the aqueous MnCO slurry, from the reaction mixture, is put in a 1000-milliliter graduate and allowed to stand therein undisturbed for seven minutes. During this time, the MnCO therein settles to the bottom forming (with a small amount of entrapped NaCl-containing mother liquor) the lower of two distinct layers, the upper layer being the major portion of the mother liquor. The volume of the low layer, comprising the MnCO and the entrapped mother liquor is then recorded in milliliters and the weight of MnCO in the lower layer ascertained by decanting oif substantially all the upper layer, filtering, washing, and drying the MnCO in the lower layer, and weighing the resulting dried filter cake. The actual weight of MnCO thus obtained is both the amount in grams, the lower layer, and the density of the slurry in the reaction vessel in grams per liter.

The ratio of the density of the body of stirred sus pension in the reaction vessel in grams per liter to the volume of the MnCO and entrapped mother liquor making up the lower layer of the Stratified 1000-milliliter sample is then ascertained and is converted to grams per cubic inch by multiplying the density in grams per cubic centimeter by 16.4, the value of (2.54) since 1 inch equals about 2.54 centimeters. The resulting answer is substantially the density of the MnCO in grams per cubic inch. For example, if the weight of MnCO in the lower layer is 60 grams (which is also the density in grams per liter) and the volume of the lower layer of MnOO and entrapped mother liquor is 80 milliliters, then the above procedure may be expressed:

60 X 16.4 or 12.3 and, therefore, the density of the MnCO is about 12 grams per cubic inch.

Since this density would be too low, in practice the soluble manganous salt and soluble carbonate aqueous X164 or 20.5

which represents a very acceptable density of 20 grams per cubic inch-for the MnCO product A second satisfactory and more convenient way of determining the bulk density of the MnCO made, which may be carried out by visual observations. and calculations only, is as follows: a 1000-milliliter sample of the aqueous MnCO slurryis obtained from the reaction mixture and put in a 1000-milliliter graduate, as above.v The total weight of thesample is'ascertainedby: obtaining the crystal density of MnCO from the table of a standard handbook (it being 3.12 grams per cmfi); obtaining the density of the upper stratified mother liquor solution in gram-s per cm. by means of an hydrometer; and measuring the volume of the settled MnCO in the 1000-rnilliliter graduate by visual observation. The total weight of the sample'is then obtained by the equation:

wherein W is the. total weightof MnCO and mother liquor in the 1000-milliliter sample; 1- is the crystal density of MnCOg; 'X is the true volume occupied by MnCO in milliliters (not the apparent or, visually measurable volume) in the 1'000-millilite-r'sample; p2 is the density of and X can be expressed as pl p2 the true volume of MnCOg.

Thebulk density is found by the equation:

P1X D- Vm where D is the bulk density of the MnCO in grams per cm. and V is the measured settled volume of the MnCO in cm. in the 1000-milliliter graduate.

Since 1 inch'=2.54 cm., the density in grams per cm. can be converted to grams per in. by multiplying it by When a satisfactory bulk density for the MnCO being made has been obtained, the feed rates and agitation are thereafter held substantially constant and the upper part of the slurry in the reaction vessel caused to overflow, in a continuous manner, into areceiving trough or conduit which preferably carries it to a settling tank. A substantial portion of the mother liquor is removed, usually continuously, from the upper part of the settling tank and the wet slurry from the lower part from which it is conveyed to a filter. The MnCO is washed, removed from the filter, and thereafter dried and (as desired) stored or used.

The following example is illustrative of the practice of the invention:

Example 1 The vessel employed was a 60-gallon glass lined kettle provided with an anchor-type agitator and a recycle pump and. return line (which provided circulation, from the bottom to the top of the kettle). An enclosing jacket was connected to hot .and cold water sources for heating and cooling, as needed- A pH'meter was positioned in the recycle line so that the pH value could be ascertained at any time. The kettle was provided with two metered feed line sand an overflow line which were equipped with suitable flow control means. The recycle line was provided with a means for obtaining samples of the reaction mixture.

of 187 grams per liter, was admitted through one of thefeed lines to the reactor, and simultaneously therewith, an aqueous solution of Na CO at a concentration of 104 grams per liter, was admitted through the other feed line. The rate of flow was continuously metered by a rotameter positioned in each feed line. The rate of in flow of the aqueous M1101 solution was 0.737 liter (1.095 gram moles) per minute. The rate of inflow of the aqueous Na CO solution was 1.095 liters (1.075 gram moles) per minute; a total inflow rate of 1.832 liters per minute was thus provided. 7

After a period of 1.5 hours, a settling test of the slurry was taken and the density of the MnCO therein found to be 12.2 grams per cubic inch. At that time, about 30 gallons of the slurry were removed from the kettle, filtered, and the MnCO on the filter returned to the kettle to build up the solids. After 3.15 hours from the start-up, a second settling test was run on the slurry and the density of the MnCO therein found to be 25 grams per cubic inch. The slurry so removed was, as above, filtered, and the MnCO collected in thefilter and returned to the kettle to build up further the solids. After 4.5 hours from the start-up, a third settling test was run and the density of the MnCO found to be 27 grams per cubic inch. At that time, another 30 gallons of the slurry were removed from the kettle, the MnCO separated by filtration and returned to the kettle to continue to build up the solids. After a total time of 5.25 hours from the start-up, another settling test was run which showed the density of the MnCO to be 23.0 grams per cubic inch. Provision was then made for overflow from the kettle at the rate of about 29 gallons per hour. The overflow was continuously filtered and the MnCO therefrom retained, washed, and dried. A settling test was run after 9.15 hours (total operating time) and showed the MnCO to have a density of 26 grams per cubic inch.

The run was continued for a total time of 30.1 hours during which 490 pounds of MnCO having an average density of 24.5 grams per cubic inch, were made. The average inventory time of the reactants in the kettle, following the initial 5.15 hours, was 1.2 hours;

During the run of Example 1, MnCO was produced in suspension at the rate of 1.075 moles per minute. This was 123.5 grams per minute, which was 67.4 grams per liter of reaction mixture. NaCl was produced in solution at the rate of 2.15 gram moles per minute. This was 125.8 grams per minute or 68.6 grams per liter. A total of 2.3 grams or 1.28 grams per liter of the. Mn portion of the MnCl remained unreacted. This represents an efficiency, in the yield of MnCO based on the weight of MnCl of 98.0%. The pH value was controlled throughout the run at between 6.0 and 6.2. The temperature was controlled throughout the run atbe: tween C. and C.

The MnCO so made was tested for the following alkaline materials which were found to be present as follows: NaHCO trace; NaOH and Na CO none. A trace of NaCl was found. It was also analyzed for the impurities normally associated therewith when made by conventional processes, which :were found in thearnounts stated in Table I below:

Reference to the analytical results, as represented by Example 4 the values set out in Table I shows that the MnCO produced was not only of a high bulk density, but was also in a high state of purity.

It should be borne in mind that that part of the pro- 5 cedure of Example 1 which comprised drawing otf excessive portions of the slurry, filtering it, and returning the thus collected MnCO to the reaction vessel is merely an expedient for building up the solids relatively rapidly.

MnCO made according to Example 1 was employed to make MnO by heating the MnCO in air to form a dense, free-flowing MnO powder. This air-oxidized product was then contacted with dilute sulfuric acid and heated to leach out any unconverted MnCO and lower oxides of manganese. The leached product was washed, dried and used to form the cathode mix of a Leclanch For purposes of comparison the following test run was A cell battery according to standard formulation. The made: battery so made was then sub ected to a standard drain Aqueous Solutions of Mhcl2 and co were test in accordance with the standard testing procedure demixed in a reaetioh Vessel at about The PH was scribed in Mlhtary Spec1ficat1on S.C.L. 3175 of the United 6.3. 754 grams of MnCO product were formed which States Army slghal P that hes}, the electronic) were separated, washed, dried, and analyzed The pred trve force of the battery bemg tested is measured as a net Showed a contamination of Nazcos, and function of drain time. The same procedure was followed NaHCO The alkalinity was unsatisfactory. The bulk 115mg M1102 P p from 8 60111111011 eommerelal 10W d i was 153 grams Per bi i h bulk denslty MnCO for comparative purposes. The re- 690 grams of the product so made were admixed with suits are shown in Table II.

TABLE II Density Density A cell After 3 mos.

of of MnOz Percent Percent cathode, Time in hrs. Time in hrs. storage time Source of MnCOa MnCO trom MnO Mn wt. in to 1.0 v. at 75 to 1.13 v. at 7.5 in hrs. to 1.13 v.

gm./in. 3 MnCO gm. ma. 1 drain 2 ma. 1 drain 3 at 7.5 ma. 1

drain 3 Example 1 24. 5 91. 8 59. 4 9.8 6. 6 167 159 Commercial 4. 4 s. 2 87. 5 5s. 4 7. 9 3 37 15 1 ma. means milliamps. At a fixed resistance of 16.7 ohms. 3 At a fixed resistance of 167 ohms.

1250 milliliters of water and heated, accompanied by Example 4 shows a significant advantage of employing stirring, to 59 C. The pH value (which was 8.6 after high density, high purity MnCO according to the invenheating) was adjusted by additional MnCl solution to tion to make MnO for dry cells over currently available 6.35. The mixture was then cooled to room temperature MnO (made from MnCO made according to convenand the MnCO product, separated, washed, and dried. tional practice).

An alkalinity analysis was run and the product found 40 Having described our invention, what we claim and deto contain 25% NaHCO The product had'a bulk sire to protect by Letters Patent is:

density of 13.5 grams per cubic inch. 1. The method of making high density MnCO of high The MnCO during its formation according to the purity which comprises admixing an aqueous solution of invention, grows dentritically, to a desirably high dena water-soluble manganous salt with a water-soluble carsity material of relatively low surface area and high bonate in amounts of each to provide and maintain a molar percent Mn, the latter indicating its purity. The MnCO excess of the Mn fraction of the manganous salt over the of the invention has a surface area of less than 5 square CO fraction of the carbonate at a pH value of between meters per gram and a Mn content of at least 44% after 5.7 and 7.2, under stirred conditions, at a temperature of drying at 110 C. The MnCO made according to Exbetween about 55 C. and the boiling temperature of the ample 1 had a surface area of less than 0.3 square meter admixture to produce MnCO in suspension to make a per gram as determined by the standard B.E.T. method slurry; maintaining the MnCO in suspension until the employing the liquid nitrogen absorption principle. It particle size and concentration of the suspended MnCO was 44.4% after drying at 110 C. in slurry are such as to insure a bulk density of the MnCO of at least 15 grams per cubic inch; and separating the Example 2 MnCO so made.

The procedure of Example 1 above was repeated eX- eept that the temperature was maintained at between perature of the reaction mixture is maintained between 52' C. and 61 C., the pH value was held at between about ahd about 6.8 and 6.9, and the run was continued (being stirred The method aeeofdlng 6121111 1 Wh reln the molar and recycled) for only 50 minutes before the MnCO 6O ratio of P to CO3 PV by h mahgaheus Salt and being f d Showed a total alkalinity, Calculated as carbonate in the reaction mixture is more than 1 but not NaHCO to be 0.2, and portions of the slurry were not more than about drawn off, filtered, and the MnCO on the filter returned m h aeofdihg to Claim 1 WheIeih the P to the reaction vessel. This is' :barely acceptable and Value 15 malhtalhed between about and about 6.9.

' shows the advantage of operating at a slightly lower pH 65 The method h h to elalm 1 wherein the M11003 and a higher temperature, and for a longer time as in being produced is maintained 1n suspension until a bulk Example 1. density tnereof of at least 20 grams per cubic inch is Example 3 assured.

6. The method according to claim 1 wherein individual streams of aqueous solutions of the manganous salt and the carbonate are metered; a portion of the slurry is drawn The procedure of Example 2 was repeated except that the temperature was held at between "52 and 58 C., the

pH value between 6.6 and 7.0, and the run continued off from the lower part of the reaction mixture and re- (being stirred and recycled) for 1 hour and 30 minutes. turned to the upper part thereof; the pH value of the t-hus The total alkalinity of the MnCO product, calculated as recycled slurry is continuously measured; an overflow of NaHCO was 0.0590. This shows that a longer reaction time than that of Example 2 gives a better product.

slurry is collected from the reaction mixture; overflow slurry so removed is passed through a filter whereby 2.- The method according to claim 1 wherein the temr 7 8 MnCO is removed therefrom and replaced in the reaction OTHER REFERENCES mixture to increase the density thereof to at least about Mellon comprehfinsive Treatise on Inorganic and 80 grams per liter; and thereafter recovering MnCO of acceptable quality in a continuous process from subsequently collected overflow from the reaction mixture.

Theoretical Chemistry, vol. 12, Longmans, Green and 5 Company, New York, 1932, pages 433 and 434.

References Cited by the Examiner OSCAR R, VERTIZ, Primary Examiner.

UNITED STATES PATENTS BENJAMIN HENKIN, Examiner.

1,889,021 11/1932 Kobe 2361 3,011,867 12/1961 Welsh 23-61 10 G. OZAKI,AssistantExaminer. 

1. THE METHOD OF MAKING HIGH DENSITY MNCO3 OF HIGH PURITY WHICH COMPRISES ADMIXING AN AQUEOUS SOLUTION OF A WATER-SOLUBLE MANGANOUS SALT WITH A WATER-SOLUBLE CARBONATE IN AMOUNTS OF EACH TO PROVIDE AND MAINTAIN A MOLAR EXCESS OF THE MN FRACTION OF THE MANGANOUS SALT OVER THE CO3 FRACTION OF THE CARBONATE AT A PH VALUE OF BETWEEN 5.7 AND 7.2, UNDER STIRRED CONDITIONS AT A TEMPERATURE OF BETWEEN ABOUT 55* C. AND THE BOILING TEMPERATURE OF THE ADMIXTURE TO PRODUCE MNCO3 IN SUSPENSION TO MAKE A SLURRY; MAINTAINING THE MNCO3 IN SUSPENSION UNTIL THE PARTICLE SIZE AND CONCENTRATION OF THE SUSPENDED MNCO3 IN SLURRY ARE SUCH AS TO INSURE A BULK DENSITY OF THE MNCO3 OF AT LEAST 15 GRAMS PER CUBIC INCH; AND SEPARATING THE MNCO3 SO MADE. 